1. FIELD OF THE INVENTION
The present invention relates to an antenna system comprising a side-looking array antenna, or more in particular to an antenna system which is capable of spatial beam scanning with a simple construction.
2. DESCRIPTION OF THE RELATED ART
It is often necessary to effect a spatial high speed scanning of an antenna beam for the purpose of receiving an electromagnetic wave from various directions and sending it in various directions such as in an antenna system used for a radar. In such a case, a multiplicity of antenna elements are generally arranged in the same plane to make up an array antenna, and the phases of the electrical signals for sending electromagnetic waves, respectively, supplied to antenna elements are varied according to a predetermined rule thereby to effect an electrical beam scanning in a phased array system. When beam scanning, effected in the phased array or the like, is not provided, on the other hand, a plurality of antennas corresponding to a plurality of desired beam directions are respectively provided and switched for operation.
In the above-mentioned phased array system, the phase of each antenna element is varied, and therefore each antenna element is required to be connected with a phase shifter. This results in an increased connection loss or transmission loss, thereby deteriorating the antenna characteristics. Further, due to the added weight of the phase shifter, generally the whole antenna system becomes heavy and bulky. In an antenna system which does not effect beam scanning, it is necessary to provide as many antennas as the desired number of beam directions. As a result, a great number of antennas are required, thereby posing the problem of connection loss, transmission loss and the weight and bulkiness of the system as in the case of phased array system.